1. Field of the Invention
The present invention relates to a process for coating a film with a thin smooth coating layer wherein the coating material is first deposited on the film with a coating roller and then regularly distributed and smoothed over the surface of the film to provide a thin uniform coating layer. The invention also relates to a device for carrying out this process.
2. Description of the Prior Art
In one known type of process for applying coatings, a large-diameter coating roller applies a rough and relatively thick layer of the coating on the film and this layer is subsequently evenly distributed and proportioned with a sheet of air to provide a relatively thin and smooth coating layer.
However, this class of coating technique cannot be used for coating at high speeds with emulsions or solutions having viscosities in excess of about 100 centipoises because of the mechanical restraints caused by the very considerable disturbance of the coating during the smoothing procedure. Moreover, when applied to specific applications, such as coating of polyvinylidene chloride on a polyester film, smoothing of the coating at high speeds with a sheet of air gives the coating "an orange skin" appearance and creates inclusions of air which impair the impermeability of the coating.
French Pat. No. 1,475,130 describes a process for coating a film utilizing a large-diameter roller with smoothing of the coating perfected using a rotating rod of much smaller diameter.
However, this process has been only marginally successful, if at all, for coating porous supports such as paper, but has not been at all successful in high-speed coating applications and particularly with respect to plastic films having a width of at least one meter. Moreover, this technique results in a "screen effect" on the coated film due to the irregularity of the coating and, accordingly, this process has not been acceptable for a majority of the applications to which coated films are utilized.